Safety paper



May 30, 1933. B. w $M|TH 1,911,774

SAFETY PAPER Filed Jan. 29, 1931 UNITED MANUFACTURlNG Co.

ANYWHERE, u.s.A. No.

PAY TO THE.

ORDEROF 313 FIRST NATIONAL BANK ANYWHERE, U.5.A.

INVENTOR BURGESS W. 5MITH ATTORNEY Patented May 30, 1933 UNITED STATES PATENT OFFICE BURGESS W. SMITH, OF ROCHESTER, INC., ROCHESTER, NEW

SAFETY PAPER Application filed January 29, 1981. Serial No. 512,196.

I This invention relates to safety paper for making bank checks and other instruments representing monetary value or for any other reason requiring protection against fradulent alteration, and more particularly to the variety of such paper which contains a sensitive or active ingredient or substance adapted to react with the usual chemical eradicating means, so as to develop a tell tale color change and thus indicate an attempted alteration.

one object of the invention is to provide a paper of this character containing an improved sensitive material capable of developing a conspicuous color change, in a reliable and positive manner, upon the application to the paper of any of the usual chemical eradicators in either an acid or alkaline condition.

Another object is to provide paper of the class described containing a sensitive material adapted to develop by reaction, as described, and of such a nature as to be particularly indelible and permanent after such reaction. More specifically stated, one of the objects of the invention is to provide such a paper containing a sensitive material having an ingredient capable of protecting one or more of the component active substances from eradicating fluid of one type, such as an acid, but without interference with its reaction to an eradicating fluid of a different type, such as an alkali.

Still a further object is the provision of a safety paper of the nature described containing a sensitive substance in the nature of a varnish or other vehicle which is itself inherently reactive with an eradicator to develop an indicating color change.

49 To these and other ends the invention resides in certain combinations and improvements hereinafter more fully described, the novel features being pointed out in the appended claims.

In the drawing:

Fig. 1 shows a bank check illustrating one mode of application of the invention, and

Fig. 2 is a similar view showing a portion of a bank check with a modified application 50 of the invention.

Safety papers have heretofore been used embodying different active ingredients tending to develop a stain or color in reaction with chemical ink eradicating means, but these ingredients have generally proven inadequate to meet the various exacting requirements of safety paper used for making bank checks, such as stability against normal influences, intensity of color change produced, the indelibility of the developed itlitin or color, low cost of production, or the A substance which is satisfactory in many respects for such purposes is that known as p.p'-dihydroxydiphenyl, more briefly known as diphenol, which is characterized by two enzene rings or groups of benzene rings, linked together with the diphenyl or equivalent linkage, and having two hydroxyl radicals in the para position to that linkage. The simplest form embodying the characteristics of the above structure or nucleus is that mentioned above, but this substance is represented also by more complex forms as, for example, p,p'-dihydroxyd1phenyl sulfide and p,p-d1hydroxydiphenylthiourea, and the variant forms embodying this nucleus or structrim may be used, provided the linkage of such rings is not so varied as to destroy the diphenyl characteristics. Such substances are referred to herein by the term diphenol substance which is employed herein and in the appended claims as including all such forms having essentially the characteristic structure or nucleus described above, as well as their substitution products, analogues, homologues, and derivatives.

The simplest form of such substances referred to above, diphenol, is preferable because it is practicable to manufacture at a low cost and high degree of purity. Convenient methods of use are to dissolve this sub stance in alcohol or make it into a water solution of one of its salts, preferably the sodium salt. Such solutions may be used to impreg- 95 nate the paper by addition to the pulp, or by passing the paper web through a bath of it, or including it in the sizing, or in other ways which will readily suggest themselves to those skilled in the art, either with or without regenerating the original phenol by action of an acid. Fig. 1 of the drawing s ows a bank check having a general stain 5 as it would be developed by the use of an eradicator in such applications of the invention. The exact formula of such solutions is a matter of choice, the intensity of the reaction color being in proportion to the amount which is used, so that the proportions employed are dependent in obvious ways upon the particular substances used, the kind of paper employed and mode of application fliereto, the depth of color desired and the Such diphenol substances may likewise be made into an ink with suitable varnish or other vehicles commonly used for such purposes, or celluloid dissolved in diacetone alcohol, or triacetin may be used, in proportions suitable to the particular printing process or apparatus. Such ink may be used to coat or print the surface of the paper, in WhOlG' or in part or with some inherent warning symbol, adapted to develop a conspicuous color in reaction with an eradicator.

Fig. 2 of the drawing shows a bank check having a background 6 printed on the paper with an ink in accordance with the present invention so as to leave unprinted portions 7 forming the letters of a warning symbol, the background being developed by the application of an eradicator.

When an eradicator is applied to. such diphenol substances, as, for example, hypochlorite of soda, they develop a pronounced bright orange or brown stain in case the hypochlorite is acid, and a pronounced dark stain in case the hypochlorite is alkaline as when used alone without preliminary appli cat-ion of an acid. Such substances have the limitation, however, that skillful application of alkaline hypochlorite in an excessive amount tends to bleach out the dark stain first developed.

It has been found that this deficiency in safety paper containing such diphenol sub stances may be satisfactorily overcome by incorporating in the paper also a substance capable of reacting with alkaline hypochlorite to develop an indelible stain. It has been found that an ideal group of substances adapted for use in combination in this man ner with diphenol substances, is that represented by diphenylguanidine, its substitution products, analogues, homologues, and derivatives, which are included herein under the designation diphenylguanidine substance. This substance is characterized by the development of a pronounced purple brown stain in reaction with alkaline hypochlorite, while its reaction with acid hypochlorite develops a lesser stain.

For the purpose of impregnating the paper, it is preferred to sulphonate the diphenylguanidine and employ its sodium salt diphenol gives a which is soluble in water and compatible with a solution of the diphenol sodium salt, especially with a slight excess of alkali. While it is believed that the mixture of these solutions forms an addition complex that is soluble in alkali, the mixture is quite as effectual as if such a compound were not formed. Paper so impregnated, by additlon to the pulp or coating the web or otherwise, may be immediately dried or-preferably passed through a mild acid solution, such as acetic acid, which neutralizes the excess of alkali, and if sufficient is absorbed, all of the alkali is eliminated, leaving the mixture neutral or acidic and only slightly soluble in water.

A particular advantage of the combination of diphenol and diphenylguanidine substances is that such a material does not form a yellow stain when dried by heat like that formed by all primary aromatic amines hitherto used for this purpose. In case it is desired to employ an ink for printing a warning symbol or other matter on the paper, with or without impregnating the latter, the above combination of substances is particularly advantageous for the purpose.

Ordinarily an ink made from a chemical reacting effectively in an acid condition only, and another chemical reacting only in an alkaline condition, with one of the usual vehicles, produces a stain of only apart of the desired intensity because under either condition of reaction, a part only of the material is active. The above material, however, is active in either acid or alkaline hypochlorite. Furthermore it has been found that the diphenylguanidine substance may be used to form a varnish vehicle which is in itself active, so that the use of an inert varnish may be avoided to further increase the degree of reaction or color development with the eradicator.

That is to say, it has been found that many of the salts of diphenylguanidine, and particularly the acetate and hydrochloride, at very strong concentration in an acid water solution are viscous and gummy, having the general characteristics of an ink varnish.

Use of such a varnish thus provides a material which is active in all its ingredients. Thus when alkaline hypochlorite is used, as an eradicator, the diphenylguanidine varnish itself produces a pronounced stain, as well as the accompanying diphenol substance. When acid hypochlorite is used the pronounced stain supplemented by the color change produced in the diphenylguanidine varnish.

A suitable ink for this purpose, in its simplest form, is made from a varnish composed of a 60% solution of diphenylguanidine lactate, with or without glycerine or its equivalent, to which diphenol is added to form an ink of the requisite consistency when proper- 1y ground together. Such an ink yields the color changes with hypochlorite in either an acid or alkaline condition, as described above.

In the use of the familiar eradicating means comprising a preliminary acid solution and a subsequent alkaline hypochlorite solution, where the acid solution be first ap-. plied and then blotted oil the paper, there is a tendency to dissolve out a suflicient pro portion of the very soluble diphenylguanidine to reduce its intensity when developed, and at the same time insuiiicient acid is supplied to insure full development of t e diphenol, with the result that the subsequent alkaline development may be reduced, particularl with an excess application of the hypochlbrite. To meet this particular condition, it is preferred to incorporate in the material an acid compatible with it, such as lactic, phthalic, citric, or benzoic, in which case a varnish is made as follows:

Diphenylguanidine 42 gm. Glacial acetic acid 20 gm. Water 4 cc.

To which is added:

This mixture has the consistency of a medium oil varnish and may be used as suggested in making an ink of any desired consistency with diphenol as a solid or pigment, in the proportion of equal parts by weight of the varnish and diphenol. Such ink reacts with either acid or alkaline eradicators, since the incorporated acid does not interfere with the normal development of the diphenylguanidine, while it is suificient to cause the diphenol to develop its orange color under all ordinary conditions as it is in intimate contact with it.

Instead of the use of acetate of diphenylguanidine to form a varnish like constituent, as above described, satisfactory results have also been secured with a mixture of phthalic acid and diphenylguanidine which is a rather insoluble material of unknown composition, resistant to acid but quickly affected by alkaline hypochlorite.

I is preferred, however, to achieve a similar esult by another method which, under "various conditions, yields a more pronounced intensity of stain. This comprises combining diphenylguanidine substance with a fatty or resin acid and dissolving the resulting soap in triacetin, ethylene glycol, glycerine or similar substances. Thus by heating and dissolving an excess of diphenylguanidine in the fatty acids of linseed oil, the base of a suitable varnish may be made that will dissolve in triacetin to the consistency of medium litho varnish, and inks may be made by grinding therein the proper amount of diphenol, for which purpose substantially equal parts of the varnish and diphenol have been. found to be suitable proportions.

Similarly, a soap may be made with rosin, oleic, stearic, or palmitic acids and the saponifiable component of shellac, carnaiiba wax, and the like, the choice being a matter of the attaining of certain known physical characteristics which may be desired in the inks to be made.

Again, these diphenylguanidine soaps may be made by double decomposition of the hydrochloride of diphenylguanidine and the alkali soap of the acids desired.

It has been found that the preliminary application of the acid of the 'eradicator serves to form a protective film about the diphenylguanidine, but just as soon as the alkalinity of the hypochlorite solution neutralizes the acidity the characteristic purple brown stain will develop. Of course, in the presence of a material amount of acid, the

diphenol will develop into the stable orange yellow.

By sulphonating diphenylguanidine and dissolving it in caustic alkali, an addition complex of diphenylguanidine is formed when mixed with a caustic alkali solution of diphenol. By theaddition of acids, such as hydrochloric, and heat, a sticky mass may be collected which can be dissolved with heat in triacetin to form a varnish which may be used alone or in combination with any of the aforesaid constituents of their chemical and physical equivalents for this purpose.

As an additional precaution against the use of an acid such as oxalic, when used aloneas an eradicator, the colorless or slightly colored base of a dye, such as alkali blue, may be incorporated, in such inks as are alkaline in reaction, or the acidity of which is of such a nature as will not develop alkali blue when it is in its colorless form. Alkali blue is rendered practically colorless by diphenylguanidine or even magnesium or zinc oxide, but upon application of even a weak acid,

.a pronounced blue color is developed.

The invention thus provides a safety paper embodying an active material which is highly sensitive to practically all chemical eradicators in either acid or alkaline condition, to develop an intense and conspicuous color change or stain, of a highly indelible nature, which material may be employed at a'low cost to either uniformly coat or impregnate the paper, or to form effective inks for printing the paper, for example, with inherent Warning symbols adapted to afford a striking indication of any attempted'crasurc of matter written on the paper.

I claim:

1. A safety paper containing a material comprising a substance having two carbon rings or groups of carbon rings linked together with the diphenyl or equivalent linkage and having two hydroxyl radicals in the para position to such linkage, and a diphenyl-guanidine substance, and adapted to react with chemical eradicators to develop a conspicuous stain.

2. A safety paper containing a material comprising a salt of a substancehaving two carbon rings or groups of carbon rings linked velop a conspicuous stain.

4. A safety paper containing a material comprising a salt of a substance having two benzene rings or groups of benzene rings linked together with the diphenyl or equivalent linkage and having two hydroxyl radicals in the para position to such linkage, and a diphenylguanidine substance, and adapted to react with chemical eradicators to develop a conspicuous stain.

5. A safety paper containing a material comprising a substance having two benzene rings or groups of benzene rings linked together with the diphenyl or equivalent linkage and having two liydroXyl radicals in the para position to such linkage, and a diphenylguanidine substance, one of said substances being of a viscous consistency and capable of serving as a printing ink vehicle for said material, said material being adapted to react with chemical eradicating means to develop a pronounced color change.

6. A safety paper containing a material comprising a salt of a substance having two benzene rings or groups of benzene rings linked together with the diphenyl or equivalent linkage and having two hydroxyl radicals in the para. position to such linkage, together with a salt of a diphenylguanidine substance, one of said salts being of a thick consistency and capable of serving as a vehicle for said material, said material being adapted to react with ch mical eradicating means to develop a conspicuous stain.

7. A safety paper containing a material comprising a. substance having two benzene. rings or groups of benzene rings linked together with the diphenyl or equivalent linkage and having two hydroxyl radicals in the para position to such linkage, a diphenylguanidine substance, and an ingredient effective to preserve one of said substances against a given eradicator solution but ineffective as against a different eradicator solution, said material being capable of developing a pronounced color change in reaction with chemical eradicating means.

'8. A safety paper containing amaterial comprising a substance having two benzene rings or groups of benzene rings linked together with the diphenyl or equivalent linkage and having two hydroxyl radicals in the para position to such linkage, a diphenylguanidine substance, one of said substances being of a viscous consistency and capable oi serving as a printing ink vehicle for said material, and an ingredient eflective to preserve one of said substances against a given eradicator solution but ineffective as against a. different eradicator solution, said material being capable of developing a pronounced color change in reaction with chemical eradicating means.

9. A safety paper containing a material comprising a substance having two benzene rings or groups of benzene rings linked together with the diphenyl or equivalent linkage and having two hydroxyl radicals in the para position to such linkage, a diphenylguanidine substance, and a printing ink vehicle, said material being adapted to react with chemical eradicator-s to develop a conspicuous stain.

10. A safety paper containing a material comprising a substance having two benzene 'rings or groups of benzene rings linked together with the diphenyl or equivalent linkage and having two hydroxyl radicals in the para position to such linkage, and a salt of a diphenylguanidine substance reduced to the viscous consistency of a printing ink vehicle, said material being adapted to react with chemical eradicators to develop a conspicuous stain.

11. A safety paper containing a material comprising a substance having two benzene rings or groups of benzene rings linked together with the diphenyl or equivalent linkage and having two hydroxyl radicals in the para position to such linkage, a salt of a diphenylguanidine substance having the viscous consistency of a printing ink vehicle and an acid ingredient operating to protect one of said substances against a given eradicator solution but ineffective as against a different eradicator solution, said material being capable of developing a pronounced color change in reaction with chemical eradicators.

12. A safety paper printed with an ink comprising an active varnish vehicle capable of reacting with chemical eradicating means to develop a conspicuous stain.

13. A safety paper having one or more inhercntly warning symbols printed thereon with a material comprising a substance having two benzene rings or groups of benzene rings linked together with the diphenyl or equivalent linkage, and having two hydroxyl radicals in the para position to such linkage, and a diphenylguanidine substance, said material being adapted to react with chemical eradicators to render said warning symbol conspicuously visible.

14. A safety paper having printed thereon one or more inherently warning symbols with a material comprising a substance having two benzene rings or groups of benzene rings linked together with the diphenyl or equivalent linkage and' having two hydroxyl radicals in the para position to such linkage, and a diphenylguanidine substance, one of said substances being of a viscous consistency capable of serving as a printing ink vehicle for said material, said material being adapted to react with chemical eradicating means to render-said warning symbols conspicuously visible.

15. A safety paper having printed thereon one or more inherently warning symbols with a material comprising a substance having two benzene rings or groups of benzene rings linked together with the diphenyl or equivalent linkage, and having two hydroxyl radicals in the para position to such linkage, a diphenylguanidine substance, and an ingredient effective to preserve one of said substances against a given eradicator solution but ineffective as against a different eradicator solution, said material being capable of developinga pronounced color change in reaction with chemical eradicating means.

16. A safety paper containing a material comprising asubstance having two benzene rings or groups of benzene rings linked together with the diphenyl or equivalent linkage and having two hydroxyl radicals in the para position to such linkage, and a diphenylguanidine soap, said material being adapted to react with chemical eradicators to develop a conspicuous stain.

17. A safety paper containing a material comprising a substance having two benzene rings or groups of benzene rings linked together with the diphenyl or equivalent linkage and having two hydroxyl radicals in the para position to such linkage, and a fatty acid soap of diphenylguanidine, said material being capable of reacting with chemical eradicating means to effect a pronounced color change.

18. A safety paper containing a material comprising a substance having two benzene rings or groups of benzene rings linked together with the diphenyl or equivalent linkage and having two hydrox l radicals in the para position to such linkiige, and a resin acid soap of diphenylguanidine, said material being capable of reacting with chemical eradicating means to effect a pronounced color change.

19. A safety paper containing a material comprising a substance having two benzene rings or groups of benzene rings linked together with the diphenyl or equivalent linkage and having two hydroxyl radicals in the para position to such linkage, and a triacetin solution of a soap of diphenylguanidine, said material being substantially changed in color by a chemical eradicating means,

20. A safety paper containing a material comprising a substance having two benzene rings or groups of benzene rings linked together with the diphenyl or equivalent link-' age and having two hydrozyl radicals in the para position to such linkage, and an ethylene glycol solution of a soap of diphenylguanidine, said material being substantially changed in color by a chemical eradicating means.

21. A safety paper containing a material comprising a substance having two benzene rings or groups of benzene rings linked together with the diphenyl or equivalent linkage and having two hydroxyl radicals in the para position to such linkage, and a glycerin-e solution of a soap of diphenlyguanidine, said material being substantially changed in color by a chemical eradicating means.

22. A safety paper containing a material comprising a diphenol substance and a diphenylguanidine substance and; adapted to .react with chemical eradicators to develop a conspicuous stain.

23. safety paper containing a material comprlslng a salt of a diphenol substance and a diphenylguanidine substance and adapted to react with chemical eradicators to develop a conspicuous stain.

24. A safety paper containing a material comprising a diphenol substance and a salt of a diphenylguanidine substance, and adapted to react with chemical eradicators to develop a conspicuous stain.

25. A safety paper containing a material comprising a salt of a diphenol substance and a salt of a diphenylguanidine substance and adapted to react with chemical eradicators to develop a conspicuous stain.

26. A safety paper containing a material comprising a diphenol substance, and a diphenylguanidine substance, one of said substances being of a viscous consistency and capable of serving as a printing ink vehicle for said compound, said material being adapted to react with chemical eradicating means to develop a pronounced color change.

27. safety paper containing a material comprising diphenol substance, and a diphenylguanidine substance, and an ingredient effective to preserve one of said substances against a given eradicator solution but ineffective as against a different eradicator solution, said material being capable of developing a pronounced color change in reaction with chemical eradicating means.

28. A safety paper containing a material comprising a salt of a diphenol substance, and a salt of a diphenylguanidine substance,

and an acid ingredient for preserving one of said substances against a given eradicator solution, said material being capable of developing a pronounced color change in reaction with chemical eradicating means,

29. A safety paper containing amaterial comprising a diphenol substance and a solution of a diphenylguanidine soap, said material being adapted to react with chemical eradicators to develop a conspicuous stain,

30. A safety paper containing a material comprising a salt of a diphenol substance and a fatty acid soap of diphenylguanidine, said material being capable of reacting with chemical eradicating means to efi'ect a pronounced color change.

31. A safety paper containing a material comprising a salt of a diphenol substance and a resin acid soap of diphenylguanidine, said material being capable of reacting with chemical eradicating means to effect a pronounced color change. 7

BURGESS W. SMITH. 

